code: def df_daily():
      """Defines a dataframe with values from a sequence,
      so it's easy to track lagged values."""
      df = pd.DataFrame(
          {
              "ts": pd.date_range(
                  start="2021-01-01", periods=314, freq="D"
              ),
              "y": list(range(314)),
          }
      )
      df_train = df.iloc[:300].reset_index(drop=True)
      df_test = df.iloc[300:].reset_index(drop=True)
      return {"df_train": df_train, "df_test": df_test}
  
imports: from datetime import timedelta
  import numpy
  import pandas
  import pytest
  from dateutil.relativedelta import relativedelta
  from testfixtures import LogCapture
  from greykite.common.constants import ERR_STD_COL
  from greykite.common.constants import LOGGER_NAME
  from greykite.common.constants import PREDICTED_COL
  from greykite.common.constants import PREDICTED_LOWER_COL
  from greykite.common.constants import PREDICTED_UPPER_COL
  from greykite.sklearn.estimator.lag_based_estimator import LagBasedEstimator
label_desc: Use image node_id 1 for calling a global function with example usage: df_daily() and returns: dict